Microfabrication Based On Electrostatic-induced Lithography

Electrostatic-Induced Lithography (EIL) is a novel microstructure formationmethod which makes use of the electrohydrodynamic instability of the film. Theshape as well as the aspect ratio of the fabricated microstructures are absolutelydetermined and limited by the mold, but can be fexibly controlled by carefullyadjusting the process parameters. Moreover, the exposure, developing, etchingprocess are not required in the process,but smooth surface profle microstructure canbe abtained by one-step pattern formation rapidly. These advantages play animportant role in the application in technologies such as micro-electro-mechanicalsystems, microfluidic devices, photonics, biomedical, genetics, tissue engineering etal.There are many parameters which play the important roles in EIL process.Researchers both at home and abroad have not studied the effect of the parameterson the process completely.This dissertation puts forward spacial electrical fieldmodulation method based on the theory of the electrohydrodynamic behavior,describes the process using the finite difference method and the finite elementmethod in detail, analyses the effect of the the duty ratio, the aspect ratio, thedistance between the template and the substrate, the thickness of the polymer,applied voltage etc. on the EIL process. Finally, the fabrication of themicro-structures with high fidelity by using optimum parameters and patterned template are finished by EIL method.The structures obtained by EIL reported so far are mostly regular structures withuniform size, including column array and grating like structures. But the irregularstructures with non-uniform size are more desirable for most microdevices.Therefore, this dissertation explores the manufacture of the grating structures withnon-uniform size and the binary zone-plate array through the proposed EIL, in anattempt to expand the applicability of the EIL approaches. In order to betterunderstand the EIL process, the works done in this dissertation include:(1) Builds an electrohydrodynamic model to describe the EIL process with flattemplate, based on a linear stability analysis theory with the lubricationapproximation. Microfabrication of the periodic columns in a large area using anunpatterned template (i.e. a flat template) is the physical foundation for the generalEIL process. The relationship between the process parameters and the size or thegrowth rate of periodic columnar microstructure is presented by analytical equations.Finally, this dissertation puts forward the method to decrease the size and increasethe growth rate of periodic columnar microstructure.(2)For the EIL using a patterned template, a spatially and temporally varyingelectric field drives the electrohydrodynamic microstructuring. So the analyticalphysical model can not be established to describe this EIL process, as in the case ofthe EIL using an unpatterned template. So, the finite difference method and the finiteelement method are used to analyse the EIL process in this dissertation in detail.We find that the thin film forms sinusoidal profiles which replicate the patternedmask initially, regardless of the parameters of the mold. In the presence of suffcientmaterial, the fnal pattern morphology is determined by the partial coalescence of theinitial columnar morphology. This dissertation concludes that the replication processhas three stages. Firstly, separated column array is first formed under the template;then, the coalescence of the column structure starts; finally, the replica of thetemplate is obtained.(3) In the EIL process, polymer is both affected by linear stability theory of the unpatterned template and modulation of the electric field owing to the patternedtemplate. In order to increase the modulation degree of the electrical field, thisdissertation puts forward that increasing the aspect ratio, the duty ratio of polymerthickness and the applied voltage, reducing the distance between the template andthe substrate can effectively produce the microstructure with high aspect ratio.(4) Fabricates microstructures in nickel with high aspect ratio up to2:1bymeans of UV-LIGA process and fabricates gratings, binary zone-plate array, squarepillar arrary, microlens array etc. by means of EIL method. Their high aspect ratiosreach up to above4:1.